Power electronics packaging is required by almost all areas of power electronics applications, such as consumer electronics, automotive, aircraft, and military applications. Due to the significant heat dissipation from the switching behavior of power semiconductor devices, the interactions between thermal, electrical and mechanical aspects become very important to not only power electronics packaging design, but also long-term reliability of power modules. The interactions become more and more significant as the development of wideband gap power semiconductor devices has pushed the power modules to be able to operate at higher voltage levels, higher ambient temperature and higher switching frequencies. Power module development relies more and more on Finite Element Method (FEM) based multiphysics simulations, reducing design cycles, to couple the electrical, thermal and mechanical fields in simulations of different processes such as power module assembly, operations and reliability assessments. In this paper, several cases were introduced to demonstrate how multiphysics simulation worked in power module development. The first case was the simulation of the fringing effects to estimate the difference between practical parasitic capacitance value and theoretical parasitic capacitance value of double-side metallized ultra-thin ceramic. The second case was the pre-stress analysis of power module substrate made of a specific ultra-thin ceramic. The third case was the study of electrical field distribution and temperature distribution in a high voltage and high temperature Silicon Carbide power module. The last case was parasitics extraction of a PCB busbar for 50 kW Electric Vehicle Motor Drive Applications.